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The synthesis and characterization of a stable, acyclic two-coordinate silylene, Si­(SAr^Me₆)₂ [Ar^Me₆ = C₆H₃-2,6­(C₆H₂-2,4,6-Me₃)₂], by reduction of Br₂Si­(SAr^Me₆)₂ with a magnesium­(I) reductant is described. It features a V-shaped silicon coordination with a S–Si–S angle of 90.52(2)° and an average Si–S distance of 2.158(3) Å. Although it reacts readily with an alkyl halide, it does not react with hydrogen under ambient conditions, probably as a result of the ca. 4.3 eV energy difference between the frontier silicon lone pair and 3p orbitals

Presentación

A reaction between imines and anhydrides has been developed with chiral disubstituted anhydrides and chiral imines. The synthesis of highly substituted γ-lactams with three stereogenic centers, including one quaternary center, proceeds at room temperature in high yield and with high diastereoselectivity in most cases. Enantiomerically pure alkyl-substituted anhydrides proceed with no epimerization, thus providing access to enantiomerically pure penta-substituted lactam products

Reversible Complexation of Lewis Bases to Low-Coordinate Fe(II), Co(II), and Ni(II) Amides: Influence of the Metal, Donor Ligand, and Amide Substituent on Binding Constants

The binding constants of several monodentate Lewis bases (L) having different donor atoms [L = tetrahydrofuran (THF), tetrahydrothiophene (THT), pyridine, 4-(dimethylamino)­pyridine (DMAP), PMe₃, PCy₃, and 1,3-bis­(1,3,5-trimethylphenyl)­imidazol-2-ylidene (IMes)] to the linear two-coordinate bis­(amido) transition-metal complexes, M­{N­(SiMe₃)­Dipp}₂ [M = Fe (<b>1</b>), Co (<b>2</b>), and Ni (<b>3</b>)] were determined by electronic absorption spectroscopy. In addition, ¹H NMR spectroscopy was used to study the complexation of M­{N­(SiMe₃)­Dipp}₂ by THF. The binding constants of the less bulky amido complexes [M­{N­(SiMe₃)₂}₂]₂ (M = Fe or Co; the nickel species is unstable) were also measured and found to bind THF 10²–10³ times more strongly than M­{N­(SiMe₃)­Dipp}₂. Furthermore, unlike the corresponding −N­(SiMe₃)­Dipp complexes, where the iron species are more strongly complexed than those of cobalt, the −-N­(SiMe₃)₂ species [Co­{N­(SiMe₃)₂}₂]₂ displayed a higher binding constant to THF than [Fe­{N­(SiMe₃)₂}₂]₂, which is in agreement with the stronger association of the [Co­{N­(SiMe₃)₂}₂]₂ dimer in comparison to that of its iron analogue. The binding strengths of the ligands to <b>1</b>–<b>3</b> were found to be in the order of DMAP > pyridine > PMe₃ > PCy₃ ≈ IMes > THF > THT, and those of the respective metals were in the order of Fe > Co > Ni

Enantiocontrol with a Hydrogen-bond Directing Pyrrolidinylsilanol Catalyst

A new bifunctional catalyst containing a silanol group has been designed and synthesized with high enantioselectivity in three steps. The hydrogen-bonding properties of this pyrrolidinylsilanol have been investigated using NMR binding studies and electrospray ionization mass spectrometry (ESI-MS) analysis. The ability of the silanol group to activate an electrophile and afford enantiocontrol through hydrogen-bond directing effects has been demonstrated using an enantioselective aldol reaction with isatin and acetaldehyde, affording up to 88% ee

Enantiocontrol with a Hydrogen-bond Directing Pyrrolidinylsilanol Catalyst

A new bifunctional catalyst containing a silanol group has been designed and synthesized with high enantioselectivity in three steps. The hydrogen-bonding properties of this pyrrolidinylsilanol have been investigated using NMR binding studies and electrospray ionization mass spectrometry (ESI-MS) analysis. The ability of the silanol group to activate an electrophile and afford enantiocontrol through hydrogen-bond directing effects has been demonstrated using an enantioselective aldol reaction with isatin and acetaldehyde, affording up to 88% ee

Reduction of Terphenyl Co(II) Halide Derivatives in the Presence of Arenes: Insertion of Co(I) into a C–F Bond

Reduction of [(3,5-^<i>i</i>Pr₂-Ar*)­Co­(μ-Cl)]₂ (3,5-^<i>i</i>Pr₂-Ar* = -C₆H-2,6-(C₆H₂-2,4,6-^<i>i</i>Pr₃)₂-3,5-^<i>i</i>Pr₂) with KC₈ in the presence of various arene molecules resulted in the formation of a series of terphenyl stabilized Co­(I) half-sandwich complexes (3,5-^<i>i</i>Pr₂-Ar*)­Co­(η⁶-arene) (arene = toluene (<b>1</b>), benzene (<b>2</b>), C₆H₅F (<b>3</b>)). X-ray crystallographic studies revealed that the three compounds adopt similar bonding schemes but that the fluorine-substituted derivative <b>3</b> shows the strongest cobalt-η⁶-arene interaction. In contrast, C–F bond cleavage occurred when the analogous reduction was conducted in the presence of C₆F₆, affording the salt K­[(3,5-^<i>i</i>Pr₂-Ar*)­Co­(F)­(C₆F₅)] (<b>4</b>), in which there is a three-coordinate cobalt complexed by a fluorine atom, a C₆F₅ group, and the terphenyl ligand Ar*-3,5-^<i>i</i>Pr₂. This salt resulted from the formal insertion of a putative 3,5-ⁱPr₂-Ar*Co species as a neutral or anionic moiety into one of the C–F bonds of C₆F₆. Reduction of [(3,5-^<i>i</i>Pr₂-Ar*)­Co­(μ-Cl)]₂ in the presence of bulkier substituted benzene derivatives such as mesitylene, hexamethylbenzene, <i>tert</i>-butylbenzene, or 1,3,5-triisopropylbenzene did not afford characterizable products

Reduction of Terphenyl Co(II) Halide Derivatives in the Presence of Arenes: Insertion of Co(I) into a C–F Bond

Reduction of [(3,5-^<i>i</i>Pr₂-Ar*)­Co­(μ-Cl)]₂ (3,5-^<i>i</i>Pr₂-Ar* = -C₆H-2,6-(C₆H₂-2,4,6-^<i>i</i>Pr₃)₂-3,5-^<i>i</i>Pr₂) with KC₈ in the presence of various arene molecules resulted in the formation of a series of terphenyl stabilized Co­(I) half-sandwich complexes (3,5-^<i>i</i>Pr₂-Ar*)­Co­(η⁶-arene) (arene = toluene (<b>1</b>), benzene (<b>2</b>), C₆H₅F (<b>3</b>)). X-ray crystallographic studies revealed that the three compounds adopt similar bonding schemes but that the fluorine-substituted derivative <b>3</b> shows the strongest cobalt-η⁶-arene interaction. In contrast, C–F bond cleavage occurred when the analogous reduction was conducted in the presence of C₆F₆, affording the salt K­[(3,5-^<i>i</i>Pr₂-Ar*)­Co­(F)­(C₆F₅)] (<b>4</b>), in which there is a three-coordinate cobalt complexed by a fluorine atom, a C₆F₅ group, and the terphenyl ligand Ar*-3,5-^<i>i</i>Pr₂. This salt resulted from the formal insertion of a putative 3,5-ⁱPr₂-Ar*Co species as a neutral or anionic moiety into one of the C–F bonds of C₆F₆. Reduction of [(3,5-^<i>i</i>Pr₂-Ar*)­Co­(μ-Cl)]₂ in the presence of bulkier substituted benzene derivatives such as mesitylene, hexamethylbenzene, <i>tert</i>-butylbenzene, or 1,3,5-triisopropylbenzene did not afford characterizable products

Enantiocontrol with a Hydrogen-bond Directing Pyrrolidinylsilanol Catalyst

A new bifunctional catalyst containing a silanol group has been designed and synthesized with high enantioselectivity in three steps. The hydrogen-bonding properties of this pyrrolidinylsilanol have been investigated using NMR binding studies and electrospray ionization mass spectrometry (ESI-MS) analysis. The ability of the silanol group to activate an electrophile and afford enantiocontrol through hydrogen-bond directing effects has been demonstrated using an enantioselective aldol reaction with isatin and acetaldehyde, affording up to 88% ee

Facile C–H Bond Metathesis Mediated by a Stannylene

The diarylstannylene, :Sn­(Ar^<i>i</i>Pr4)₂ (Ar^<i>i</i>Pr4 = C₆H₃-2,6-(C₆H₃-2,6-^<i>i</i>Pr₂)₂), undergoes C–H metathesis with toluene, <i>m</i>-xylene, or mesitylene in solutions of these solvents at 80 °C. The products, [Ar^<i>i</i>Pr4Sn­(CH₂Ar)]₂ (Aryl=C₆H₅ (<b>1a</b>), C₆H₄-3-Me (<b>1b</b>), C₆H₃-3,5-Me₂(<b>1c</b>)) were characterized via ¹H, ¹³C and ¹¹⁹Sn NMR, UV–vis and IR spectroscopy, and by X-ray crystallography for <b>1a</b> and <b>1b</b>. A stoichiometric amount of the arene, Ar^<i>i</i>Pr4H, was also produced in these reactions. The use of EPR spectroscopy indicated the presence of a new type of one-coordinate, tin-centered radical, :ṠnAr^<i>i</i>Pr4, resulting from Sn–C bond cleavage in Sn­(Ar^<i>i</i>Pr4)₂

Enantiocontrol with a Hydrogen-bond Directing Pyrrolidinylsilanol Catalyst

A new bifunctional catalyst containing a silanol group has been designed and synthesized with high enantioselectivity in three steps. The hydrogen-bonding properties of this pyrrolidinylsilanol have been investigated using NMR binding studies and electrospray ionization mass spectrometry (ESI-MS) analysis. The ability of the silanol group to activate an electrophile and afford enantiocontrol through hydrogen-bond directing effects has been demonstrated using an enantioselective aldol reaction with isatin and acetaldehyde, affording up to 88% ee